In many machines carrying out a sequence of operations involving rapidly rotating and/or reciprocating parts it is essential for effective functioning of the machine that the parts be in the correct positions with reference to each other at certain defined points in the machine cycle. The procedure of moving the machine parts to their correct positions is known as "setting the timing". This is usually done by accurately positioning by hand a reference mark on one part of the machine against a reference mark on another part whilst the machine is effectively stationary. This is an expensive time-consuming operation and has to be repeated from the beginning if it is suspected that the timing of the machine has altered. Further, if a machine is stationary while its timing is being set, the effects of back-lash and wear in components may well alter the effective timing when the machine is running under load.
It is an object of the present invention to provide a means by which the timing of a rotating or reciprocating machine part may be investigated easily without the effects of back-lash or wear throwing doubt on the result of the investigation.